The present invention relates to helical gear pumps, and more particularly, to helical gear pumps in which a portion of the stator extending into an inlet chamber has been modified to improve the material handling capability of the pump.
A typical helical gear pump, or progressing cavity pump, comprises a rotor having one or more externally threaded helical lobes which coact with a stator having an internal bore extending axially therethrough, where the bore includes a plurality of helical grooves (one more helical groove than the number of helical lobes of the rotor). Pumps of this general type are typically built with a rigid metallic rotor and a stator which is formed from a flexible or resilient material such as rubber. The rotor is made to fit within the stator bore with an interference fit, i.e., there is a compressive fit between the rotor and stator. This compressive fit results in seal lines where the rotor and stator contact. These seal lines define or seal off definite cavities bounded by the rotor and stator surfaces. As the rotor turns within the stator, the cavities defined by the seal lines progress from the suction end of the pump to the discharge end of the pump.
Typical progressing cavity pumps can be used to pump a wide range of fluids including fluids with solids in suspension, high viscosity fluids, and shear sensitive fluids; and since pumps of this type are positive displacement pumps, they can pump fluids with entrained gases without vapor locking.
A disadvantage with typical progressing cavity pumps is that it is often-times difficult to introduce certain materials (i.e., fluids with entrained solids or highly viscous fluids) into the individual cavities during the pumping operation. For example, a common phrase heard in the industry is, "if only we can get that product into the pump elements, it would pump."
One known method for transporting the materials to the pump elements is with the use of augers to convey a product horizontally towards the pump elements. However, such means are only marginally effective, and further, it does not significantly improve upon the introduction of heavily viscous fluids into the pump elements. Various mechanical devices have been used in an attempt improve the feeding of viscous fluids into progressing cavity pumps. Devices such as bridge breakers or paddle pushers have been installed directly in the suction housings. Other devices, such as AugMentor or twin screw feeders have been added to the suction housings, but these devices often only marginally improve the feeding of material to the rotor and stator.
Accordingly, a need exists for a progressing cavity pump system having an improved solids handling capability and improved capability of handling viscous materials. Additionally, there is a need for a progressing cavity pump system with an improved means for introducing the materials being pumped into the cavities formed by the pump elements.